Integrated  Circuit Having a Vertical Power MOS Transistor

ABSTRACT

A device includes a vertical transistor and a lateral transistor on a substrate, wherein the vertical transistor comprises a first gate in a first trench, a second gate in a second trench, a source and a drain, wherein the source and the drain are on opposite sides of the first trench and the lateral transistor and the drain are on opposite sides of the second trench.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.15/413,271, entitled “Integrated Circuit Having a Vertical Power MOSTransistor,” filed on Jan. 23, 2017, which is a continuation of U.S.patent application Ser. No. 14/846,753, entitled “Integrated CircuitHaving a Vertical Power MOS Transistor,” filed on Sep. 5, 2015 andissued as U.S. Pat. No. 9,553,029 on Jan. 24, 2017 which is a divisionalof U.S. patent application Ser. No. 13/588,070, entitled “IntegratedCircuit Having a Vertical Power MOS Transistor,” filed on Aug. 17, 2012and issued as U.S. Pat. No. 9,130,060 on Sep. 8, 2015 which is acontinuation-in-part of U.S. patent application Ser. No. 13/546,506,entitled “Apparatus and Method for Power MOS Transistor,” filed on Jul.11, 2012 and issued as U.S. Pat. No. 8,669,611 on Mar. 11, 2014, all ofwhich applications are incorporated herein by reference.

BACKGROUND

The semiconductor industry has experienced rapid growth due toimprovements in the integration density of a variety of electroniccomponents (e.g., transistors, diodes, resistors, capacitors, etc.). Forthe most part, this improvement in integration density has come fromshrinking the semiconductor process node (e.g., shrink the process nodetowards the sub-20 nm node). As semiconductor devices are scaled down,new techniques are needed to maintain the electronic components'performance from one generation to the next. For example, lowgate-to-drain capacitance and low on resistance of transistors may bedesirable for power applications. In addition, it is desirable tointegrate vertical power transistors with lateral power transistors on asame semiconductor die.

As semiconductor technologies evolve, metal oxide semiconductor fieldeffect transistors (MOSFET) have been widely used in today's integratedcircuits. MOSFETs are voltage controlled devices. When a control voltageis applied to the gate a MOSFET and the control voltage is greater thanthe threshold of the MOSFET, a conductive channel is established betweenthe drain and the source of the MOSFET. As a result, a current flowsbetween the drain and the source of the MOSFET. On the other hand, whenthe control voltage is less than the threshold of the MOSFET, the MOSFETis turned off accordingly.

MOSFETs may include two major categories. One is n-channel MOSFETs; theother is p-channel MOSFETs. According to the structure difference,MOSFETs can be further divided into two sub-categories, namely trenchpower MOSFETs and lateral power MOSFETs. In an n-channel trench powerMOSFET, a p-body region is employed to form a channel coupled betweenthe source region formed over the p-body region and the drain regionformed under the p-body region. Furthermore, in the trench power MOSFET,the drain and source are placed on opposite sides of a wafer. There maybe a trench structure comprising a gate electrode formed between thedrain and the source of the trench power MOSFET.

Trench power MOSFETs are commonly known as vertical power MOSFETs.Vertical power MOSFETs have widely used in high voltage and currentapplications due to their low gate drive power, fast switching speed andlower on resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a cross sectional view of a semiconductor devicecomprising a quasi-vertical trench MOS transistor in accordance with anembodiment;

FIG. 2 illustrates a cross sectional view of a semiconductor devicecomprising a plurality of quasi-vertical MOS transistors in accordancewith an embodiment;

FIG. 3 illustrates a cross sectional view of a semiconductor devicecomprising a quasi-vertical MOS transistor in accordance with anotherembodiment;

FIG. 4 illustrates a cross sectional view of a semiconductor devicecomprising a plurality of quasi-vertical MOS transistors in accordancewith another embodiment;

FIG. 5 illustrates a cross sectional view of a semiconductor deviceafter an N-type epitaxial layer and an NBL layer are formed over asubstrate in accordance with an embodiment;

FIG. 6 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 5 after a dielectric layer is formed over the substrateand a plurality of ion implantation processes are applied to thesemiconductor device in accordance with an embodiment;

FIG. 7 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 7 after a hard mask layer is formed over the substrate inaccordance with an embodiment;

FIG. 8 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 7 after suitable etching processes are applied to thedielectric layer and the hard mask layer in accordance with anembodiment;

FIG. 9 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 8 after etching processes are applied to the N-typeepitaxial layer in accordance with an embodiment;

FIG. 10 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 9 after a dielectric deposition process is applied to thefirst trench and the second trench in accordance with an embodiment;

FIG. 11 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 10 after an etching process is applied to the oxide layerin accordance with an embodiment;

FIG. 12 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 11 after a hard mask removal process is applied to the topsurface of the semiconductor device in accordance with an embodiment;

FIG. 13 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 12 after a gate dielectric layer is formed in the trenchas well as the top surface of the semiconductor device in accordancewith an embodiment;

FIG. 14 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 13 after a gate electrode layer is formed in the trenchand a plurality of gate electrodes are formed on the top surface of thesemiconductor device in accordance with an embodiment;

FIG. 15 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 14 after a variety of ion implantation processes areapplied to the top surface of the semiconductor device in accordancewith an embodiment; and

FIGS. 16-27 illustrate intermediate steps of fabricating thesemiconductor device including a quasi-vertical trench MOS transistor100 shown in FIG. 3 in accordance with an embodiment.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the embodimentsof the disclosure, and do not limit the scope of the disclosure.

The present disclosure will be described with respect to embodiments ina specific context, an integrated circuit having a quasi-vertical powermetal oxide semiconductor (MOS) transistor device and a plurality oflateral MOS transistors including high voltage MOS transistors and lowvoltage MOS transistors. The embodiments of the disclosure may also beapplied, however, to a variety of semiconductor devices. Hereinafter,various embodiments will be explained in detail with reference to theaccompanying drawings.

FIG. 1 illustrates a cross sectional view of a semiconductor devicecomprising a quasi-vertical trench MOS transistor in accordance with anembodiment. The semiconductor device 10 includes four regions, namely afirst region 100 for forming a quasi-vertical trench MOS transistor, asecond region 200 for forming a high voltage NMOS device having ascalable channel length, a third region 300 for forming a high voltagePMOS device, a fourth region 400 for forming a low voltage NMOS deviceand a fifth region 500 for forming a low voltage PMOS device. Each ofthe regions 100, 200, 300, 400 and 500 are defined by isolation regionssuch as shallow trench isolation (STI) regions 101. Alternatively, fieldoxides can be formed as isolation regions.

The quasi-vertical trench MOS transistor 100 includes a substrate 102with a first conductivity type. In accordance with an embodiment, thefirst conductivity type is P-type. The quasi-vertical trench MOStransistor 100 further includes an N-type buried layer (NBL) 104 formedover the substrate 102 and an N-type epitaxial layer 106 formed over theNBL layer 104. The quasi-vertical trench MOS transistor 100 furthercomprises a first trench comprising an oxide region 110 and a gateregion 112. As shown in FIG. 1, the gate region 112 is formed over theoxide region 110. The quasi-vertical trench MOS transistor 100 mayfurther comprise a P-type body (PB) region 108 formed in the N-typeepitaxial layer 106, a P+ region 126, a first N+ region 122 and a secondN+ region 124.

As shown in FIG. 1, the P+ region 126 and the first N+ region 122 areformed in the PB region 108. The second N+ region 124 is formed in theN-type epitaxial layer 106. In accordance with an embodiment, the firstN+ region 122 is a source region of the quasi-vertical trench MOStransistor 100. The second N+ region 124 is a drain region of thequasi-vertical trench MOS transistor 100. The PB region 108 is a channelcoupled between the source and drain of the quasi-vertical trench MOStransistor 100. As shown in FIG. 1, the first N+ region 122 and thesecond N+ region 124 are formed on opposite sides of the gate region112. The second N+ region 124 functions as the drain region, which iscoupled to the channel region (PB region 108) through the N-typeepitaxial layer 106 and the NBL layer 104.

The quasi-vertical trench MOS transistor 100 comprises a second trenchhaving a same depth as the first trench. In particular, the secondtrench comprises a deep trench 114 and an accumulation layer (not shown)formed along the sidewall of the deep trench 114. As shown in FIG. 1,the second trench is formed adjacent to the second N+ region 124. Inaccordance with an embodiment, the deep trench 114 may be electricallycoupled to the gate region 112. When a gate control voltage is appliedto the gate region 112 as well as the deep trench 114, the gate controlvoltage may attract majority carriers and generate the accumulationlayer (not shown) along the sidewall of the deep trench 114. Theaccumulation layer may be of more majority carriers. As a result, a lowresistance drain current conductive path is built between the NBL layer104 and the second N+ region 124.

As shown in FIG. 1, despite that the N-type epitaxial layer 106 cancarry the drain current from the NBL layer 104 to the second N+ region124, the resistance of the N-type epitaxial layer 106 is higher than theaccumulation layer formed along the sidewall of the deep trench 114. Byemploying an accumulation layer coupled between the second N+ region 124and the NBL layer 104, the current transport is improved. In addition,by coupling the NBL layer 104 with the second N+ region 124, the draincurrent can be picked up from the NBL layer 104. As a result, the drainof the quasi-vertical trench MOS transistor 100 can be placed at thesame side as the source.

One advantageous feature of the quasi-vertical MOS transistor 100 isthat the quasi-vertical structure shown in FIG. 1 can be easilyintegrated into lateral fabrication processes. Another advantageousfeature of the quasi-vertical MOS transistor 100 is that theaccumulation layer formed along the sidewall of the second trench helpsto provide a low on resistance channel for the drain current. As aresult, the on resistance of the MOS transistor 100 is improved despitethat a quasi-vertical structure is employed.

FIG. 1 further illustrates the semiconductor device 10 including aplurality of lateral devices, which are integrated on a samesemiconductor substrate (P-type substrate 102) as the quasi-vertical MOStransistor 100. The high voltage NMOS device 200 includes a deep P-Well202 formed in the N-type epitaxial layer 106. Likewise, the high voltagePMOS device 300 includes a deep P-Well 302. The low voltage NMOS device400 and the low voltage PMOS device 500 share a deep P-Well 402. Asshown in FIG. 1, the deep P-Wells 202, 302 and 402 are formed in theN-type epitaxial layer 106 and separated each other by isolation regions101 and portions of the N-type epitaxial layer 106 between two adjacentdeep P-Wells. The lateral devices 200, 300, 400 and 500 may includeother wells, drain/source regions and gate electrodes. The detailedfabrication steps of the lateral devices will be described below withrespect to FIGS. 5-15.

One advantageous feature of having the quasi-vertical MOS transistor 100shown in FIG. 1 is that the quasi-vertical MOS structure can beintegrated with lateral MOS devices on a same substrate. As such, theexisting lateral device fabrication process may be reused. The existinglateral device fabrication process helps to reduce the cost offabricating the quasi-vertical MOS transistor 100.

FIG. 2 illustrates a cross sectional view of a semiconductor devicecomprising a plurality of quasi-vertical MOS transistors in accordancewith an embodiment. The structure of the semiconductor device 20 issimilar to the structure of the semiconductor device 10 shown in FIG. 1except that a deep trench is employed to provide a low on resistancechannel for the drain currents of a plurality of quasi-vertical MOStransistors. In particularly, FIG. 2 illustrates a deep trench providinga low on resistance channel for two quasi-vertical MOS transistorsconnected in parallel. It should be noted that the deep trench may becapable of providing a conductive channel for a number of quasi-verticalMOS transistors, two quasi-vertical MOS transistors are illustrated forsimplicity.

FIG. 3 illustrates a cross sectional view of a semiconductor devicecomprising a quasi-vertical MOS transistor in accordance with anotherembodiment. The structure of the semiconductor device 30 is similar tothe structure of the semiconductor device 10 shown in FIG. 1 except thatthe N-type epitaxial layer can be replaced by a high voltage N-Wellformed in a P-type epitaxial layer. The detailed formation andfabrication steps of the semiconductor device 30 will be described belowwith respect to FIGS. 16-27.

FIG. 4 illustrates a cross sectional view of a semiconductor devicecomprising a plurality of quasi-vertical MOS transistors in accordancewith another embodiment. The structure of the semiconductor device 40 issimilar to the structure of the semiconductor device 20 shown in FIG. 2except that the N-type epitaxial layer can be replaced by a high voltageN-Well formed in a P-type epitaxial layer.

FIGS. 5-15 illustrate intermediate steps of fabricating thesemiconductor device including a quasi-vertical trench MOS transistor100 shown in FIG. 1 in accordance with an embodiment. FIG. 5 illustratesa cross sectional view of a semiconductor device after an N-typeepitaxial layer, an NBL layer and a plurality of isolation regions areformed over a substrate in accordance with an embodiment. As shown inFIG. 5, the NBL layer 104 is formed over the P-type substrate 102. Inparticular, the NBL layer 104 is formed in the upper left corner of theP-type substrate 102. The N-type epitaxial layer 106 is formed over theNBL layer 104 and the P-type substrate 102. As shown in FIG. 5, theremay be a plurality of isolation regions 101 formed in the N-typeepitaxial layer 106.

It should be noted while FIG. 5 illustrates the conductivity of thesubstrate 102 is P-type, it is merely an example. The substrate 102 maybe N-type. A person skilled in the art will recognize that theconductivity type of other layers may change in response to theconductivity type change of the substrate 102.

The substrate 102 may be formed of silicon, silicon germanium, siliconcarbide or the like. Alternatively, the substrate 102 may be asilicon-on-insulator (SOI) substrate. The SOI substrate may comprise alayer of a semiconductor material (e.g., silicon, germanium and thelike) formed over an insulator layer (e.g., buried oxide and the like),which is formed in a silicon substrate. Other substrates that may beused include multi-layered substrates, gradient substrates, hybridorientation substrates and the like.

The NBL layer 104 may be formed by implanting N-type doping materialssuch as phosphorous or the like into the substrate 102. Alternatively,the NBL layer 104 can be formed by a diffusion process. In accordancewith an embodiment, the NBL layer 104 is of a doping density in a rangefrom about 10¹⁹/cm³ to about 10²¹/cm³.

The N-type epitaxial layer 106 is grown from the NBL layer 104. Theepitaxial growth of the N-type epitaxial layer 106 may be implemented byusing any suitable semiconductor fabrication processes such as chemicalvapor deposition (CVD), ultra-high vacuum chemical vapor deposition(UHV-CVD) and the like. In accordance with an embodiment, the N-typeepitaxial layer 106 is of a doping density in a range from about10¹⁵/cm³ to about 10¹⁸/cm³.

The isolation regions 101 may be shallow trench isolation (STI) regions,and may be formed by etching the N-type epitaxial layer 106 to form atrench and filling the trench with a dielectric material as is known inthe art. The isolation regions 101 may be filled with a dielectricmaterial such as an oxide material, a high-density plasma (HDP) oxide,or the like, formed by conventional methods known in the art.

FIG. 6 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 5 after a dielectric layer is formed over the substrateand a plurality of ion implantation processes are applied to thesemiconductor device in accordance with an embodiment. The dielectriclayer 602 is formed over the N-type epitaxial layer 106. The dielectriclayer 602 may comprise an oxide layer. The dielectric layer 602 may beformed by any oxidation process, such as wet or dry thermal oxidation inan ambient environment comprising an oxide, H₂O, NO, or a combinationthereof, or by CVD techniques using tetra-ethyl-ortho-silicate (TEOS)and oxygen as a precursor

As shown in FIG. 6, three deep P-Wells 202, 302 and 402 are formed inthe N-type epitaxial layer 106. The deep P-Wells 202, 302 and 402 areseparated by isolation regions as well as the N-type epitaxial layer106. In accordance with an embodiment, the deep P-Wells may be of adoping concentration in a range from about 10¹⁶/cm³ and about 10¹⁹/cm³.The deep P-Wells may be formed by implanting a p-type dopant such asboron. Likewise, three high voltage N-Wells 204, 304 and 404 are formedin the deep P-Wells 202, 302 and 402 respectively. The high voltageN-Wells may be formed by implanting an n-type dopant such as phosphorusat a doping concentration in a range from about 10¹⁵/cm³ and about10¹⁸/cm³.

FIG. 6 further illustrates a 5V P-Well 206 formed in the high voltageN-Well 204, a P-type double diffusion (PDD) region 306 formed in thehigh voltage N-Well 304 and a 5V P-Well 406 formed in the high voltageN-Well 404. In accordance with an embodiment, the 5V P-Wells may be of adoping concentration in a range from about 10¹⁵/cm³ and about 10¹⁸/cm³.The PDD region 306 may be of a doping concentration in a range fromabout 10¹⁵/cm³ and about 10¹⁸/cm³. The 5V P-Wells and PDD region may beformed by implanting a p-type dopant such as boron.

FIG. 7 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 7 after a hard mask layer is formed over the substrate inaccordance with an embodiment. The hard mask layer 702 is deposited onthe dielectric layer 602 in accordance with an embodiment. The hard masklayer 702 may be formed of silicon nitride. The hard mask layer 702 isdeposited on top of the dielectric layer 602 through suitablefabrication techniques such as CVD and the like.

FIG. 8 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 7 after suitable etching processes are applied to thedielectric layer and the hard mask layer in accordance with anembodiment. The hard mask layer 702 and the dielectric layer 602 arepatterned in consideration with the location of the first trench andsecond trench of the quasi-vertical MOS transistor 100 (shown in FIG.1). Thereafter, an etching process, such as a reactive ion etch (RIE) orother dry etch, an anisotropic wet etch, or any other suitableanisotropic etch or patterning process, is performed to form theopenings 802 and 804 shown in FIG. 8. It should be noted that inaccordance with an embodiment, the width of the opening 804 is greaterthan the width of the opening 802.

FIG. 9 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 8 after etching processes are applied to the N-typeepitaxial layer in accordance with an embodiment. An etching process,such as RIE, dry etch, wet etch, or any other suitable anisotropic etchtechniques are applied to the N-type epitaxial layer 106 to form thetrench 902 and the trench 904. As shown in FIG. 9, both the first trench902 and the second trench 904 are formed in a same fabrication step.Such a single step formation of the first trench 902 and the secondtrench 904 helps to reduce the fabrication cost of the quasi verticalMOS transistor 100.

As shown in FIG. 9, the etching process may etch through the N-typeepitaxial layer 106 and partially etch the NBL layer 104. Moreover, FIG.9 illustrates that the depth of the first trench 902 is approximatelyequal to the depth of the second trench 904. It should be noted that asshown in FIG. 9, the width of the second trench 904 is greater than thewidth of the first trench 902. The relatively larger opening of thesecond trench 904 helps to maintain an opening during a subsequent oxidedeposition process. The oxide deposition process will be described indetail below with respect to FIG. 10.

FIG. 10 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 9 after a dielectric deposition process is applied to thefirst trench and the second trench in accordance with an embodiment. Asshown in FIG. 10, a dielectric layer 1002 fills the first trench 902(shown in FIG. 9), but partially fills the second trench 904. There maybe an opening 1004 in the second trench 904 after the dielectricdeposition process. As described above with respect to FIG. 9, the widthof the second opening 904 is greater than the width of the first opening902. As a result, by controlling the dielectric deposition process, thedielectric layer 1002 may partially fill the second trench 904.

In accordance with an embodiment, the dielectric layer 1002 may beformed of oxide. Throughout the description, the dielectric layer 1002may be alternatively referred to as the oxide layer 1002. The oxidelayer 1002 may be formed by using suitable thermal treatment techniques,wet treatment techniques or deposition techniques such as PVD, CVD, ALDor the like. It should be noted that the oxide layer 1002 shown in FIG.10 is merely an example. Other dielectric materials such as such asnitrides, oxynitrides, high-k materials, combinations thereof, andmulti-layers thereof may be alternatively used.

FIG. 11 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 10 after an etching process is applied to the oxide layerin accordance with an embodiment. An etching process, such as a RIE, ananisotropic wet etch, or any other suitable anisotropic etch process, isperformed to remove the upper portion of the oxide layer in the firsttrench to form the oxide layer 110 shown in FIG. 11.

Moreover, the etching process is so controlled that the oxide layer inthe second trench is fully removed. In other words, the second trench isfree from oxide. In accordance with an embodiment, the oxide layer 110shown in FIG. 11 is of a thickness H1. H1 is in a range from about 0.5um to about 5 um. It should be noted that the dimensions recited throughthe description are merely examples, and may be changed to differentvalues. It should further be noted that the oxide layer 110 shown inFIG. 11 may function as a field plate, which helps to reduce the surfaceelectrical field. Furthermore, the reduced surface electrical fieldalong the oxide layer 110 may improve the voltage rating of the quasivertical MOS transistor 100.

FIG. 12 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 11 after a hard mask removal process is applied to the topsurface of the semiconductor device in accordance with an embodiment. Asshown in FIG. 12, the hard mask layer and the oxide layers shown in FIG.11 have been removed through a suitable hard mask layer removal processsuch as a wet etch process. The removal process is applied to the topsurface of the semiconductor device until the N-type epitaxial layer 106is exposed.

FIG. 13 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 12 after a gate dielectric layer is formed in the trenchas well as the top surface of the semiconductor device in accordancewith an embodiment. As shown in FIG. 13, the gate dielectric layer 1302is formed in the first trench, the second trench as well as the topsurface of the semiconductor device. The gate dielectric layer 1302 maybe formed of commonly used dielectric materials such as oxides,nitrides, oxynitrides, high-k materials, combinations thereof, andmulti-layers thereof.

In accordance with an embodiment, the gate dielectric layer 1302 is anoxide layer. The gate dielectric layer 1302 may be formed by usingsuitable thermal treatment techniques, wet treatment techniques ordeposition techniques such as PVD, CVD, ALD or the like.

FIG. 14 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 13 after a gate electrode layer is formed in the trenchand a plurality of gate electrodes are formed on the top surface of thesemiconductor device in accordance with an embodiment. The gate region112, the deep trench 114, the gate electrodes 208, 308, 408 and 508 maybe filled with the same material through the same fabrication process.

The gate region 112, the deep trench 114 the gate electrodes 208, 308,408 and 508 may comprise a conductive material, such as a metal material(e.g., tantalum, titanium, molybdenum, tungsten, platinum, aluminum,hafnium, ruthenium), a metal silicide (e.g., titanium silicide, cobaltsilicide, nickel silicide, tantalum silicide), a metal nitride (e.g.,titanium nitride, tantalum nitride), doped poly-crystalline silicon,other conductive materials, or a combination thereof. In accordance withan embodiment, amorphous silicon is deposited and recrystallized tocreate poly-crystalline silicon (poly-silicon).

In accordance with an embodiment, the gate region 112, the deep trench114 the gate electrodes 208, 308, 408 and 508 may be formed ofpoly-silicon. The gate regions (e.g., 112, 208, 308, 408 and 508) andthe deep trench 114 may be formed by depositing doped or undopedpoly-silicon by low-pressure chemical vapor deposition (LPCVD). Inaccordance with another embodiment, the gate regions (e.g., 112, 208,308, 408 and 508) and the deep trench 114 may be formed of metalmaterials such as titanium nitride, tantalum nitride, tungsten nitride,titanium, tantalum and/or combinations. The metal gate electrode layermay be is formed using suitable deposition techniques such as ALD, CVD,PVD and the like. The above deposition techniques are well known in theart, and hence are not discussed herein.

FIG. 15 illustrates a cross sectional view of the semiconductor deviceshown in FIG. 14 after a variety of ion implantation processes areapplied to the top surface of the semiconductor device in accordancewith an embodiment. As shown in FIG. 15, the PB region 108 is formed inthe N-type epitaxial layer 106. In accordance with an embodiment, the PBregion is of a doping concentration in a range from about 10¹⁶/cm³ andabout 10¹⁸/cm³.

A plurality of spacers (not shown) may be formed for their correspondinggate electrodes. The spacers may be formed by blanket depositing one ormore spacer layers (not shown) over the gate electrodes and thesubstrate. The spacer layers may comprise SiN, oxynitride, SiC, SiON,oxide, and the like and may be formed by commonly used methods such aschemical vapor deposition (CVD), plasma enhanced CVD, sputter, and othermethods known in the art. The spacer layers may be patterned, such as byisotropically or anisotropically etching, thereby removing the spacerlayers from the horizontal surfaces of the structure and forming thespacers.

The P+ region 126 may be formed by implanting a p-type dopant such asboron at a concentration of between about 10¹⁹/cm³ and about 10²¹/cm³.The first N+ region 122 is formed over the PB region 108. In accordancewith an embodiment, the first N+ region 122 functions as the source ofthe MOS transistor 100. The source region may be formed by implanting ann-type dopant such as phosphorous at a concentration of between about10¹⁹/cm³ and about 10²¹/cm³. Furthermore, a source contact (not shown)may be formed over the first N+ region 122.

The second N+ region 124 is formed in the N-type epitaxial layer. Inaccordance with an embodiment, the second N+ region 124 may be the drainof the MOS transistor 100. The drain region may be formed by implantingan n-type dopant such as phosphorous at a concentration of between about10¹⁹/cm³ and about 10²¹/cm³. As shown in FIG. 1, the drain region isformed on the opposite side from the source (the first N+ region 122).

The P+ region 126 may be formed by implanting a p-type dopant such asboron at a concentration of between about 10¹⁹/cm³ and about 10²¹/cm³.The P+ region 126 may contact the p-type body of the MOS transistor 100.In order to eliminate the body effect, the P+ region 126 may be coupledto the first N+ region 122 (the source of the MOS transistor 100)directly through the source contact (not shown).

An inter-layer dielectric (ILD) layer (not shown) is formed over the topsurface of the semiconductor device shown in FIG. 15. The ILD layer maybe formed of silicon nitride doped silicate glass, although othermaterials such as boron doped phosphor silicate glass or the like mayalternatively be utilized. Contact openings (not shown) may be formed inthe ILD layer through an etching process. After the etching process, aportion of the ILD layer remains and becomes a gate-to-source dielectriclayer 132. In addition, conductive materials are deposited into theopening to form the source contact (not shown).

The N+ and P+ regions of lateral devices having the gate electrodes 208,308, 408 and 508 may be formed the same fabrication processes as thefirst N+ region 122, the second N+ region 124 and the P+ region 126. Theformation of the N+ and P+ regions of the lateral devices is similar tothat of the N+ and P+ regions of the quasi vertical MOS transistor 100,and hence is not discussed in further detail herein to avoid repetition.

FIGS. 16-27 illustrate intermediate steps of fabricating thesemiconductor device including a quasi-vertical trench MOS transistor100 shown in FIG. 3 in accordance with an embodiment. The fabricationsteps shown in FIGS. 16-27 are similar to the fabrication steps shown inFIG. 5-15 except that the N-type epitaxial layer shown in FIG. 5 isreplaced by a high voltage N-Well formed in a P-type epitaxial layer inFIG. 16.

As shown in FIG. 16, the semiconductor device includes a plurality ofNBL layers 104, 332, 342 and 452 formed in the substrate 102. Instead ofhaving an N-type epitaxial layer 106 shown in FIG. 5, a P-type epitaxiallayer 1602 is grown over the substrate 102. The P-type epitaxial layer1602 is of a doping concentration in a range from about 10¹⁴/cm³ toabout 10¹⁷/cm³.

FIG. 16 further illustrates a plurality of high voltage N-Wells 302,334, 344 and 454 are formed in the P-type epitaxial layer 1602. The highvoltage N-Wells 302, 334, 344 and 454 may be of a doping concentrationin a range from about 10¹⁵/cm³ to about 10¹⁸/cm³. The fabricationprocess shown in FIGS. 16-27 is similar to the fabrication process shownabove with respect to FIGS. 5-15, and hence is not discussed againherein.

Although embodiments of the present disclosure and its advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the present disclosure, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to the presentdisclosure. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps.

What is claimed is:
 1. A device comprising: a vertical transistorcomprising: a first gate in a first trench, wherein a dielectric layerand a gate region are in the first trench; a second gate in a secondtrench, wherein a bottom of the second trench is lower than a bottom ofthe gate region; a first drain/source region and a second drain/sourceregion formed on opposite sides of the first trench; and a first lateraltransistor, wherein the first later transistor and the seconddrain/source region are on opposite sides of the second trench.
 2. Thedevice of claim 1, wherein: the first lateral transistor is between afirst isolation region and a second isolation region.
 3. The device ofclaim 2, further comprising: a third isolation region between the firstisolation region and the second isolation region, wherein a firstdrain/source region of the first lateral transistor extends from asidewall of the third isolation region to a sidewall of the secondisolation region.
 4. The device of claim 3, wherein: the first isolationregion is between the second trench and a second drain/source region ofthe first lateral transistor.
 5. The device of claim 4, wherein: thefirst lateral transistor is in a semiconductor structure having a firstburied layer over a substrate, a first well over the first buried layerand a second well in the first well, and wherein: three sides of thesecond well are surrounded by the first well; and a width of the firstburied layer is substantially equal to a width of the first well.
 6. Thedevice of claim 5, wherein: the first drain/source region of the firstlateral transistor is in the first well; and the second drain/sourceregion of the first lateral transistor is in the second well.
 7. Thedevice of claim 5, wherein: a bottommost surface of the first well ishigher than a bottommost surface of the second gate.
 8. The device ofclaim 5, wherein: the first trench extends through a high voltage welland partially through a buried layer, and wherein the high voltage wellis over the buried layer.
 9. The device of claim 1, wherein: abottommost surface of the gate region is over a topmost surface of thedielectric layer, and wherein the gate region and the dielectric layerform the first gate; a width of the second trench is greater than awidth of the first trench; and a bottom of the first trench issubstantially level with a bottom of the second trench.
 10. A devicecomprising: a vertical transistor comprising: a first gate in a firsttrench, wherein the first gate comprises a dielectric layer and a gateregion over the dielectric layer; a second gate in a second trench,wherein a bottom of the second trench is substantially level with abottom surface of the first trench; a source region and a drain regionformed on opposite sides of the first trench; and a plurality of lateraltransistors, wherein the plurality of lateral transistors and the drainregion are on opposite sides of the second trench.
 11. The device ofclaim 10, wherein: two adjacent lateral transistors are separated by anisolation region.
 12. The device of claim 10, wherein: the plurality oflateral transistors includes a high voltage lateral transistor and a lowvoltage lateral transistor.
 13. The device of claim 12, wherein: adrain/source region of the high voltage lateral transistor extends froma sidewall of a first isolation region to a sidewall of a secondisolation region, and wherein a bottom of the drain/source region of thehigh voltage lateral transistor is higher than bottoms of the firstisolation region and the second isolation region.
 14. The device ofclaim 12, wherein: the high voltage lateral transistor and the lowvoltage lateral transistor are formed in two different wells over asubstrate.
 15. The device of claim 10, wherein: a sidewall of the sourceregion is in contact with a sidewall of the first trench; and a sidewallof the drain region is in contact with a sidewall of the second trench.16. A device comprising: a vertical transistor and a lateral transistoron a substrate, wherein: the vertical transistor comprises a first gatein a first trench, a second gate in a second trench, a source and adrain, wherein the source and the drain are on opposite sides of thefirst trench; and the lateral transistor and the drain are on oppositesides of the second trench.
 17. The device of claim 16, wherein: thevertical transistor is formed in a first semiconductor structureincluding a first buried layer over the substrate, a first well over thefirst buried layer, and wherein the first trench and the second trenchextend through the first well and partially through the first buriedlayer.
 18. The device of claim 17, wherein: the first gate is in anupper portion of the first trench; and the second gate extends throughthe second trench, and wherein a bottom of the first gate is higher thana bottom of the second gate.
 19. The device of claim 17, wherein: thelateral transistor is formed in a second semiconductor structureincluding a second buried layer over the substrate, a second well overthe second buried layer, and wherein a width of the second well issubstantially equal to a width of the second buried layer.
 20. Thedevice of claim 19, wherein: a bottom of the second buried layer issubstantially level with a bottom of the first buried layer; and abottom of the second well is substantially level with a bottom of thefirst well.